1. Field of the Invention
The invention relates to an improved, self-steering, auxiliary axle assembly for vehicles such as, but not limited to, heavy load-transporting vehicles such as dump trucks.
2. Background Art
In recent years, there has been considerable effort devoted to developing self-steering axle assemblies attachable to heavy trucks so that these trucks can meet governmentally imposed weight restrictions. These weight restrictions arose out of a need to minimize pavement and bridge damage due to trucks carrying heavy loads.
Maneuverability of trucks such as dump trucks, cement mixers, semi-trailers and refuse vehicles is affected by two diametrically opposed considerations. First, the federal bridge formula weight laws normally require trucks to have a relatively long wheel base and, secondly, congested job sites necessitate tight turning radii which usually require a short wheel base.
The federal bridge formula is applied for determining how much a vehicle can legally weigh and how long the vehicle must be. The formula spells out the distances required between axle groups for a given vehicle weight and is designed to protect bridges and highways by requiring a vehicle's weight to be distributed over axles spaced far apart. By so designing a vehicle, the entire weight of a vehicle is not concentrated on a short section of a bridge span or road surface.
A solution to this problem is a vehicle configured with self-steering, liftable tag axles and pusher axles. This arrangement meets the federal bridge formula by placing additional axles on the road while the vehicle is travelling to a job site. After the vehicle reaches the job site, the tag and pusher axles can be lifted for slow speed maneuvering. While the primary consideration in utilizing self-steering, tag and pusher axles is to comply with federal bridge formula standards, there is the advantage to the vehicle owner that tire scuff and frame-side loading are both reduced, while increased payload and fuel economy provide economic advantages.
One disadvantage of providing self-steering, tag and pusher axles is that they add considerable expense to the initial cost of a vehicle, as well as adding additional mechanical components which must be understood and maintained by mechanics and which, if not maintained, can eventually reduce the efficiency of the vehicle and perhaps even disable the vehicle.